1. Field of the Invention
This invention relates to internal combustion engines and is directed more particularly to an engine exhibiting improved thermal efficiencies, and to an improved method for generating power.
2. Description of the Prior Art
It is known to improve thermal efficiency of a gas turbine engine by employing a regenerative heat exchanger which operates to extract heat from combustion exhaust gases and to use the extracted heat to raise the temperature of compressed air prior to its entering the combustion chamber.
The use of heat exchangers in internal combustion engines to obtain improved thermal efficiencies, similarly to the use and improvement in gas turbine engines, is difficult because of the cyclic nature of the engine operation and the limited space inside the internal combustion engine combustion cylinder. Providing a regenerative thermal mass to receive and store heat from the combustion exhaust gas during an exhaust stroke and applying the heat to the compressed air charge, or fuel-air mixture, at the end of the compression stroke is theoretically possible but difficult in practice because of the requirement of providing sufficient heat transfer area while limiting the heat storage mass to a size suitable for disposition in the combustion space.
It is further known that spark ignition engines typically exhibit lower efficiencies than diesel engines because of the limited compression ratios of spark ignition engines. However, spark ignition engines can be made to provide efficiencies equal to those of diesel engines by employing a "more-complete-expansion" cycle. In such a cycle, the effective compression ratio is set in the 8-12 range by timing the closing of the inlet valve, while the expansion ratio is maintained in the 16-20 range. The more-complete-expansion approach is known and is used in commercially available spark ignition engines.
It is still further known that using insulated cylinder walls to reduce heat loss from the combustion gas to the ambient. air increases the power output in the expansion process. However, using insulated materials on the cylinder walls also causes the air to be heated and the compression power to increase, which counteracts the power gain in the expansion process. Therefore, the net gain in power output of the engine is low.
There is thus a need for an internal combustion engine having therein heat transfer means for extracting heat from combustion exhaust gasses and applying that heat to compressed air, or fuel-air mixture, prior to the initiation of the combustion process.
There is further a need for such an engine wherein substantially complete expansion is experienced.
There is still further a need for such an engine having a low compression ratio and a low air temperature at the end of compression and a low peak cylinder pressure, such that fuels with low octane rating do not cause engine detonation, and heavy construction, as in diesel engines, is not required, and an engine so provided is of less weight than a conventional diesel engine.
There is still further a need for an internal combustion engine having therein insulation means to reduce heat loss from the combusted gas while not causing heating of the air charge during compression.
There is still further a need for a method for generating power, which method is more efficient than previous methods utilizing internal combustion engines.